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staging heat pumps

I've recently taken over service at a local catholic church and school. They are remodeling the caffeteria and it has three split 5 ton heat pumps that i've moved but have not started up yet. I was thinking about staging them so they could save a little money when room wasn't being used which is a bout 70% of the time. If i wanted two of them on first stage and the other on stage two could I do this by running off of one 75 or 100 va transformer or should I go about this differently. I've never staged three systems before so I want to make sure the control side won't get overloaded.

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Originally Posted by buddylee

I've recently taken over service at a local catholic church and school. They are remodeling the caffeteria and it has three split 5 ton heat pumps that i've moved but have not started up yet. I was thinking about staging them so they could save a little money when room wasn't being used which is a bout 70% of the time. If i wanted two of them on first stage and the other on stage two could I do this by running off of one 75 or 100 va transformer or should I go about this differently. I've never staged three systems before so I want to make sure the control side won't get overloaded.

i would go with at least 40va per system for a total of 120va

you could parrallell two 60va x-formers, or three 40va x-formers, just make sure you phase them properly!

Each was controlled by its own stat.
Two have auxillary heat.
They are suspened approx. 15 feet apart so I was thinking about using the two on the ends as first stage and the one in the center as second stage and as heating is not really an issue i was going to wire the auxilary only as emergency.

An unoccupied cafeteria doesn’t need a lot of cooling for most of the year, when its not occupied.

I would use an IAQ thermostat. Set up the 2 outer units as stage 1 and stage 2. Then hook a delay timer that if stage 2 runs for 15 minutes, the third unit comes on.
This would give them economic operation when not occupied, and keep the humidity down while under a low sensible load.
The IAQ is quick enough that it will bring the second stage on quick enough when people/students come in for lunch.